Anticipatory control for hybrids

Something that’s been in the back of my mind came to the fore on reading this release from Clemson University. Also this project from NREL.

Variability of fuel economy with speed and torque is a given for a conventional vehicle. At one extreme, idling is a complete waste of fuel (zero mpg), and high engine speeds are also inefficient; but fuel efficiency varies widely even with vehicle speed, acceleration, hill climbing, headwinds, etc.

At a macro level, if we had perfect foresight of traffic conditions, for instance, we could choose the ‘best’ route, given constraints of desired journey time, maximum speeds, etc.

At a micro level, knowledge of neighboring vehicles’ positions, speeds and likely future positions would be helpful in navigating through traffic. This could be tied in with traffic-following cruise controls. These seem like the problems the Clemson team is tackling.

But the world of hybrids is more complicated. At any point, the control system must make a choice in balancing the energy delivered electrically or chemically. Should the ICE or the battery run the car, and when should the ICE charge the battery? The general intent is to keep the ICE operating at its optimum speed/load points, for peak fuel efficiency, as all energy used in a hybrid is ultimately chemical .

Take a long uphill stretch as an example. If the control system knew it was coming, it might ensure the battery was fully-charged at the bottom, and then depleted at a rate to reach its minimum charge at the crest, especially if the subsequent downhill would allow regenerative braking to recharge the battery.

Or, approaching a steep downhill, the system would know that regenerative braking was imminent, and could use up as much electricity as possible beforehand. If it started going downhill with a charged battery, the regenerative energy would be wasted and the friction brakes would wear more than necessary.

The two ‘bad’ conditions would be those above, either facing a high-torque requirement with a depleted battery or a regenerative event with a full one. But more than this, it should be possible to optimize the rate of battery charge/discharge if the future power requirement were known.

This cannot be too difficult for a commuting route. The road geography is the same every day, and although traffic conditions may change, I suspect they would not be too variable. In such a case, it would be possible for the driver to indicate ‘we are on the commute’, or the vehicle could just assume that since it was starting from home or the office at a given time, it would be following the usual route… for infreqent trips, the route optimizer could be linked to the sat-nav system (or even influence it) to get some idea of the geography ahead.

A GPS logger would provide all the information necessary to build a profile of the commuting route – the more difficult task would be to take that data and program the hybrid controller, but it’s just a case of modeling the power train in the hybrid, and making adjustments to the hybrid control program? We could add some settings for the desired economy/speed/performance tradeoffs, sedate-to-sporty. I would be interested to find how much difference this would make to fuel economy.